In Victorian England of the second half of the 19th century, 12 distinguished gentlemen led by Sewallis Shirley created the Kennel Club. It was the period when Mendelian laws of inheritance and the theories of Charles Darwin became popular. With the club, Shirley, MP for Westminster (like her father and grandfather before her), wanted to create the rules to determine and maintain the pedigree of the numerous dog breeds that emerged in those years. Today, with dozens of Kennel Clubs around the world and thousands more affiliated, the diversity of dog breeds (359 recognized by the International Cynological Federation, and counting) is believed to have occurred in that period. A work published in Science qualifies this idea: more than 10,000 years ago there were dogs of all shapes and sizes.
Toward the end of the last Ice Age – scientists disagree on when – humans domesticated wolves or perhaps a common ancestor of wolves and dogs, whose descendants have been with us ever since. Not even the authors of the new work clarify the doubt, nor did they intend to do so. But what they demonstrate conclusively is that at least 11,000 years ago dogs were already morphologically canines. And not only that, they also show that they had a range of shapes and sizes, perhaps not as extreme as today, but much more diverse than previously believed.
Using a quantitative and systematic method such as scanning the skulls of 643 canids, the oldest from around 50,000 years ago, and letting the machines run using three-dimensional morphometry, the authors of this study were able to map the smallest difference in shape or size of each specimen. There are archaeological sites from all over the planet, pedigrees, dozens of stray dogs or even modern wolves.
Placed on a 3D matrix, several pieces of evidence emerge. The first is that the 17 specimens from the late Pleistocene (about 11,700 years ago) about which there were doubts are “morphologically wolves”, says the study. The 374 dogs from the early Holocene (the current geological epoch) had skulls that overlapped with those of the 158 current dogs used in the sample (whether purebred, street or mixed). The first three dogs, according to their morphology, are animals found buried with their presumed owners at the site of Veretje, in present-day Russia. They had dated the oldest between 11,145 and 10,724 years before the present.
“A reduction in the size of the skull of dogs was detected for the first time between 9,700 and 8,700 years ago, while an increase in dimensional diversity appears starting from 7,700 years ago”, explains the archaeozoologist of the Institute of Evolutionary Sciences of Montpellier (France), of the CNRS, Guaranteen Evin, first co-author of the study. “Greater variability in skull shape began to emerge around 8,200 years ago,” the researcher adds in a note.
Evin goes on to say that today’s dogs “exhibit more extreme morphologies, such as brachycephalic bulldogs and long-nosed Borzoi, which are absent in early archaeological specimens.” However, he adds that “there was already great diversity among dogs in the Neolithic.” The exact figures are as follows: Early dogs were already twice as diverse as Pleistocene specimens, albeit half (52%) what they would be after the work of people like Shirley.
Francisco Gil Cano, professor of anatomy and embryology at the Faculty of Veterinary Medicine at the University of Murcia and co-author of the study, clarifies that “the work does not deny that around 200 years ago Victorian dog clubs were responsible for formalizing the selective breeding that gave rise to the hundreds of modern breeds we know today.” But he quickly adds: “What is proven is that dogs already had considerable diversity in the size and shape of their skulls more than 10,000 years ago, long before dog clubs and pedigrees existed.”
Domestic dogs are among the most morphologically diverse mammals on the planet. “From the tiny Chihuahua to the imposing Great Dane or Lion Mastiff, from the flat-nosed pug to the long-nosed greyhound. The enormous variety of shapes and sizes of today’s dogs is astonishing, with great differences especially in the morphology of their heads,” says Gil Cano. However, remember, “the dog, Canis lupus familiarisit is not the species with the greatest diversity of races; For example, there are currently more than 900 recognized cattle breeds on the planet.”
The archaeozoologist of the Autonomous University of Barcelona, María Saña, studies the first processes of domestication by humans in antiquity. “They weren’t looking for certain characteristics or profiles,” he says. It wasn’t something as conscious and direct as it would have happened in the 19th century. “They diversified as a result of encountering different ecological environments, mediated by human needs, food or the uses to which they were intended,” he adds. The moment is not random: after the last ice age, environmental conditions helped man in his expansion and, with him, that of dogs.
From the Institut Català d’Arqueologia Clàssica, researcher Lídia Colominas contributed to the work with skulls of specimens from the Iron Age and the Roman period. “This cranial diversity that we have already documented in prehistory was likely the result of a combination of environmental and human factors,” he says in an email. “Early humans influenced the animals that thrived around them, intentionally or unintentionally, but environmental and ecological pressures also played an important role,” he adds. Dogs in the Arctic regions faced very different environments and pressures than those in the tropics. “Later, as in Roman times, where a great canine morphological variability is also documented, the environmental factor must not have been so decisive, and the changes were produced by conscious anthropic selection to adapt dogs to different human needs”, concludes Colominas.
Travel companions also in the genes
One of the possible explanations for that primitive diversity would be in the expansion that humans carried out after the end of the last ice age across the planet. In fact, the ancient skulls studied have been found on every continent except Australia, where dogs only arrived with English settlers in modern times.
Another study also published in Science reinforces the idea of travel companions. This group of researchers analyzed the genome of several dozen dogs that lived in Eurasia at least 10,000 years ago, comparing it with that of today’s dogs. They showed that some of the oldest specimens traveled long distances with human groups. The connection is demonstrated at various times in prehistory. For example, when steppe dwellers brought metallurgy to China about 4,000 years ago, they brought their dogs with them.
Comparing the ancestry of different human groups and different dogs, the authors find a surprising overlap: “Eastern human populations, such as ancient Paleo-Siberians, Northeast Asians, and East Asians, were associated with dogs of East Asian or Arctic origin,” they write in the article. To add that Western human groups, “such as Iranian farmers, Caucasian hunter-gatherers and steppe herders, were associated with the Western Eurasian canine lineage.”
“This close link between human and canine genetics demonstrates that dogs were an integral part of society, whether you were a hunter-gatherer in the Arctic Circle 10,000 years ago or a metallurgist in an ancient Chinese city,” Laurent Frantz, a paleogeneticist at the University of Munich (Germany) and Queen Mary of London, says in a statement. “This is an extraordinary and long-lasting collaboration that demonstrates the enormous flexibility of the role that dogs can play in our societies, much more than any other domestic species,” concludes Professor Frantz, lead author of the study.
